Marlin 2.0.5.3 delta printer bed probing serious issue

Hi guys,
I am in the process of modifying a FLSun QQ-S delta printer to use a SKR mini E3 board for its sweet silent drivers.
This far I adapted and compiled the firmware to include bed leveling with the printer's own probe (a microswitch manually snapped underneath the nozzle with a magnet), and it compiled and flashed without issues. To be sure, I checked the probe to be working via the M119 command, which reports its correct behaviour upon triggering.

Before I launched a real probing and leveling (risking damage to the probe, the bed, the hotend, or all of the above) I tried to "fake it" manually triggering the probe when the head was still way above the bed. Of course I couldn't re-trigger it again within the accepted range for a successful probing, so the leveling failed and it displayed a message onscreen to tell me.

This is the precise point where the issue occured the first time: as soon as the probing failed, the head dashed at full speed towards the bed. I was barely quick enough to turn the whole printer off before it crashed the probe against the bed.
I was then able to reproduce the same issue a couple of times testing in mid-air, always with the same result.

For my last try I wanted to test it for real, on the bed, hoping that by probing in the accepted range the leveling would succeed. Of course, it failed immediately anyway and promptly crashed the probe on the bed surface, breaking it beyond use in the process. I ordered a replacement, but the problem is still there.

It almost seems as if the chosen behaviour for a failed probing would be to quickly home towards Z MIN, despite the homing direction configured oppositley in the firmware. But this doesn't seem right to me.


Have you guys got any idea of what could be causing this? I don't see anything in the configuration files related to this bizarre behaviour. I attached my configuration files, I could use any help you could give me.

Can you provide any update on your progress on this project? I’m attempting the same thing but a mini e3 v2.0 board

Hi! Unfortunately I was not able to find the source of the problem. I ultimately abandoned Marlin for this printer in favor of whole different firmware.